Iain Martin is a political commentator, and a former editor of The Scotsman and former deputy editor of The Sunday Telegraph. He is the author of Making It Happen: Fred Goodwin, RBS and the men who blew up the British economy, published by Simon & Schuster.. As well as this blog, he writes a column for The Sunday Telegraph. You can read more about Iain by visiting his website

The rise of Ukip is a nightmare for David Cameron

How much damage can Ukip do to the Tories? Some Conservative über-modernisers seem to have concluded that the answer is: "not very much". Given their record, which involved adherence to a strategy which resulted in a failure to beat Gordon Brown outright, I am tempted to conclude that Conservatives should now be very worried indeed.

Professor Tim Bale has said that Tories concerned about Ukip are worrying about a "daft distraction" and should aim only for the centre ground. He says the real threat to Conservative prospects will come from Labour. Well, yes, of course the next election will principally be a fight between the two largest parties. But that is only part of the story: elections have sub-plots that can turn out to have a significant impact.

At the next general election, in 2015 or earlier, it will matter what happens to the 6,836,248 Lib Dem votes from 2010. Will the party fall back to a number closer to its 5,985,454 tally in 2005, or sink even further to poll something like the 4,814,321 of 2001? After the events of the last few years, might the fall be even steeper, leaving more than two million votes up for grabs? Or will the party prove more geographically resilient in the seats it holds? In Scotland, hitherto a stronghold, it looks to be headed for oblivion.

The UK polls suggest that Labour has already hoovered up many Left-leaning Lib Dem voters, who defected when Gordon Brown was in the chair. Before the recent Budget-related excitements the Labour leadership view was that both they and the Tories were stuck at around 38 per cent and facing the same challenge: how to get to 42 per cent and an overall majority.

If that turns out to be the eventual scenario, then Cameron doesn't need a growing Ukip threat making his tricky task even more difficult. Equally, if it is worse than that for the Tories by the time of the next election, and they are now polling consistently below 35 per cent, Cameron also needs every vote he can get.

Ukip's vote is not concentrated in ways that enables it to win seats in a first past the post election system. And, say its critics, the party is not yet well-organised enough to pose a serious threat to the Tories. But the current rise of Ukip obviously matters. Tim Bale is making a common psephological error: just because something has not happened in the past does not mean that it won't at some point in the future.

Ukip scored 11 per cent in one poll last weekend. Even if that turns out to be a rogue finding, Nigel Farage's troops have been polling 7 per cent recently. Plenty of Conservatives, disgruntled with Cameron and the coalition, are currently flirting with the possibility of voting Ukip at future elections, even just as a protest. There is widespread discontent with the major parties, including amongst the kind of Tory-leaning voters Cameron needs to get back onside.

It is the steady rise of Ukip at UK general elections that should trouble the Tories. In 1997 the party polled just 105,722 votes, but the Referendum Party caused havoc for the Tories with its 811,849 votes. That showed there was a strong Eurosceptic constituency of 900,000+ voters prepared to consider alternatives to the Tories, which Ukip struggled at first to tap into. In 2001 the party moved up to 390,563, but in 2005 it was 605,973 and in 2010 it rose to 919,471. I fail to see how almost a million voters, disproportionately likely to have previously voted Tory, voting Ukip can be anything other than a serious problem for the Conservatives, particularly when Cameron fell short of an overall majority.

The question for Farage is now whether he can maintain the rate of progress of the last decade, by smashing through the million vote mark next time and pushing up towards 1.5m.

In contrast to the current über-moderniser analysis, George Osborne, as the Conservative party's election supremo, has always taken the threat seriously. Ahead of the 2008 local elections, he was obsessed with trying to ensure that Ukip did not jeopardise Tory progress against Gordon Brown. Now the Conservative leadership faces a strategic dilemma. In 2008 and in 2010 they could play the Eurosceptic card and say that Cameron was determined to govern as a robust opponent of further EU integration. To what extent will such promises be believable this time? Don't all answer at once.